'The Road Less Travelled' by M Scott Peck starts with the statement: "life is hard", as a truth to be universally acknowledged and accepted and without the acceptance of which Dr Peck believes we can not attain contentment.
Indeed, studies have shown time and time again that our expectations colour how we evaluate outcome. Recent research on patients undergoing knee surgery found out that those who were fully briefed and understood that they were likely to experience pain afterwards actually felt a lot better after the surgery than those people who did not expect any pain.
So a healthy dose of realism can actually facilitate happiness. Alter your expectations - know that you will sometimes have bad days and that you will screw up, that way when days come when things don't go your way, it isn't a surprise but just a normal part of life, a blip that can be overcome. Not everyone will like you, you won't say the right thing all the time - this is just common sense, being realistic, so why be unhappy when this happens at the expense of all the good things for which you should be happy.